1. Field of the Invention
This invention relates to the field of fluid health sensors, and particularly to microelectromechanical (MEM) devices and methods for determining the health of a fluid.
2. Description of the Related Art
Knowing the health and remaining useful life of a fluid is important in many applications. For example, fluids used in rotating machinery and hydraulic systems such as pumps, transmissions, turbines, etc., may fail or perform poorly when their operating fluids are at or near the end of their useful life. Systems damaged by the use of a degraded fluid may require costly repair or replacement, and are likely to result in unscheduled downtime.
The degradation of fluids such as liquid lubricants, engine oils, hydraulic fluids and the like, involves the simultaneous operation of a number of mechanical, chemical, and electrochemical processes. As such, no single physical metric is able to provide a high-confidence indication of fluid health or remaining useful life. Numerous methods have been employed to determine fluid health. For example, the conductivity of a fluid can be measured and plotted over time. The detection of an inflection point in the plotted measurement can indicate the end of the fluid's useful life. However, it can be difficult to detect the inflection point in the presence of noise, and there is significant variation in conductivity vs. time plots for different fluid types. As such, results obtained via this method alone can be unreliable.
Another approach is described in U.S. Pat. No. 6,852,216 to Moscaritolo et al. Here, a fluid filter employs a number of sensors to measure respective fluid parameters such as differential pressure, temperature, conductivity, viscosity, pH level, etc., with the results processed to determine the condition of the filter element. However, the described design is intended to determine the health of the filter element itself, rather than the fluid. Furthermore, each sensor is separately fabricated and packaged; providing a plurality of separate sensors in this way can be costly, require a unacceptably large amount of area, and may be unreliable.
There is a clear need for a small, inexpensive, reliable means of providing a high-confidence indication of fluid health.